Many olefin polymerization catalysts are known, including conventional Ziegler-Natta catalysts. While these catalysts are inexpensive, they exhibit low activity and are generally poor at incorporating α-olefin comonomers. To improve polymer properties, single-site catalysts, in particular metallocenes are beginning to replace Ziegler-Natta catalysts.
Catalyst precursors that incorporate a transition metal and an indenoindolyl ligand are known. U.S. Pat. Nos. 6,232,260 and 6,451,724 disclose the use of transition metal catalysts based upon indenoindolyl ligands, but have no examples using supported catalysts. While they mention that supported catalysts may be used, little information is given. They list silica and alumina as possible support materials and do not mention aluminum phosphate.
WO 01/53360 discloses open architecture indenoindolyl catalysts that may be supported on an inert support. There is no mention of aluminum phosphate as a support material. In the single example (Example 8) preparing a supported catalyst, a solution of the catalyst is added to a polyethylene support.
U.S. Pat. No. 6,559,251 discloses a process for polymerizing olefins with a silica-supported, indenoindolyl Group 4–6 transition metal complex having open architecture. U.S. Pat. No. 6,211,311 teaches that many heterometallocenes are inherently unstable and this causes difficulties in supporting these catalysts and poor catalyst activity. This problem is avoided by using chemically treated supports to prepare supported catalysts containing heteroatomic ligands. Aluminum phosphate is not mentioned. The examples use silica or alumina.
U.S. Pat. No. 6,541,583 discloses a process for polymerizing propylene in the presence of a Group 3–5 transition metal catalyst that has two non-bridged indenoindolyl ligands. None of the examples uses a supported catalyst. They state that the catalyst can be immobilized on a support and state that the support is preferably a porous material such as inorganic oxides or chlorides and polymer resins. There is no mention of aluminum phosphate.
Pending application Ser. No. 10/123,774, filed Apr. 16, 2002, discloses a process for polymerizing ethylene in the presence of a silica supported Group 3–10 transition metal catalyst that has two bridged indenoindolyl ligands. Aluminum phosphate is not mentioned and silica is the only support used.
Aluminum phosphate supports are known. U.S. Pat. No. 4,596,862 polymerizes ethylene with a catalyst comprising a chromium compound on a fluorided aluminophosphate support with a phosphorus to aluminum molar ratio of 0.15 to 0.4. In the examples, the supported catalyst is prepared by adding an aqueous solution of chromium nitrate to a hydrogel made from aluminum nitrate and ammonium dihydrogen phosphate.
U.S. Pat. No. 5,869,587 teaches an olefin polymerization process with an active catalytic component on a specific aluminophosphate support. The active catalytic component is described as any component which has activity for the polymerization of alpha-olefins and which does not interact adversely with the aluminophosphate support. However, there is no teaching as to which types of catalysts fulfill these requirements other than a statement that Ziegler type catalysts are suitable. Preferably the active catalytic component is chromium and the examples all have an aqueous solution of CrO3 impregnated on the aluminophosphate.
Despite the considerable work that has been done with catalysts based upon indenoindolyl ligands, there is a need for improvement, especially with regard to catalyst activity and comonomer incorporation. Improved catalyst activity lowers the catalyst cost per pound of polyolefin and also gives polyolefins with reduced levels of transition metal. High levels of transition metal can have a deleterious effect on properties such as thermal stability and photostability. Improved comonomer incorporation reduces polyolefin density and improves certain properties such as toughness.